Weight-loaded target carrier for laser tracking

ABSTRACT

Exemplary practice of the present invention provides a carriage including a body having a void, a vertical rod passing through the void, four legs arranged rectangularly and projecting obliquely downward and outward from the body, and a vertical coil spring coaxially encompassing a lower portion of the vertical rod. The carriage is coupled with a retroreflective laser target at the bottom of the vertical rod whereby the top of the spring pushes against the bottom of the body and the bottom of the spring pushes against the top of the target. The target continuously adjusts in height so that the bottom of the target remains in constant spring-tension contact with the surface on which the carriage sits or travels, supported by its legs. The carriage is electromechanically propelled, and laser tracking is conducted to direct laser beams at and receive laser retroreflections from the target at various surface locations. According to some inventive embodiments, one or more weights are implemented, in lieu of or in addition to a spring, to exert a downward force upon the target.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout payment of any royalties thereon or therefor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This United States patent application is related to the United Statespatent application, hereby incorporated herein by reference and beingfiled concurrently herewith, entitled “Spring-Loaded Target Carrier forLaser Tracking,” inventors Pinkesh D. Bharatia, Robert J. Santoro, andNicholas R. Cifelli.

BACKGROUND OF THE INVENTION

The present invention relates to metrology, more particularly toutilization of retroreflective targets for effecting laser tracking.

“Metrology” is a broad term referring to the science and study ofweights and measures and measurement. Three-dimensional geometries ofobjects are often measured using a coordinate measuring machine (CMM),which displays readings received from one or more probes. Numerousindustries require precise measurements of three-dimensional shapes.

A kind of CMM known as a laser tracker is prevalent in military andindustry. According to typical operation of a laser tracker, aretroreflective target is maintained in contact with an object. Anoft-used type of retroreflective target is a spherically mountedretroreflector (SMR). A laser beam is emitted by the laser tracker andimpinges upon the SMR, which reflects laser light back to the lasertracker along the original path from the laser tracker. The lasertracker includes an interferometer, which measures the distance from thelaser tracker to the SMR based on laser light that re-enters the lasertracker. The laser beam is thus tracked by the laser tracker so as tomeasure mathematical/spatial coordinates (e.g. distance and two angles)that correspond to the location of the SMR.

A conventional approach to performing laser tracking with respect to ahollow cylindrical object involves placement of a spring-loaded touchprobe to determine depth at a single point. The spring-loaded touchprobe is then removed to record the data taken and is subsequently setup again, further down the bore of the object, for another measurement.Conventional methods, such as those implementing feeler gauges andmicrometers, tend to be slow, tedious, inaccurate, and difficult torepeat without variances.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a better methodology for taking multiple measurements using alaser tracker and a retroreflective target with respect to a cylindricalor other three-dimensional object.

The present invention provides for three basic modes of practice, eachof which features, inter alia, exertion of a downward force. The firstinventive mode of practice is characterized by downward force associatedwith a spring. The second inventive mode of practice is characterized bydownward force associated with at least one weight. The third inventivemode of practice is characterized by downward force associated with acombination of a spring and at least one weight.

In accordance with exemplary practice of the present invention thatinvolves spring-loading, a laser target assembly includes a generallyrectangular member, four legs, a shaft, a coil spring, and aretroreflective target (such as a spherically mounted retroreflector).The generally rectangular member is characterized by four corners and acentral aperture extending therethrough. Each of the four legs isconnected to the generally rectangular member at a corner of therectangular member. The shaft passes through the central aperture of thegenerally rectangular member. The retroreflective target is connected tothe shaft at an axial end of the shaft. The coil spring circumscribesthe shaft so as to exert respective tensile forces against therectangular member and the retroreflective target. The laser targetassembly is positionable upon a surface (such as an inner surface of ahollow cylinder) at each of plural locations of the surface whereby thelegs and the retroreflective target are contiguous the surface. At eachlocation of the surface upon which the retrorefective target is situatethe retroreflective target is contiguous the surface in accordance withspring-loading associated with the coil spring. According to someinventive embodiments, an inventive laser tracking system includes alaser tracker and an inventive laser target assembly.

In accordance with exemplary practice of the present invention thatinvolves weight-loading, a laser target assembly includes a generallyrectangular member, four legs, a shaft, at least one weight, and aretroreflective target (such as a spherically mounted retroreflector).The generally rectangular member is characterized by four corners and acentral aperture extending therethrough. Each of the four legs isconnected to the generally rectangular member at a corner of therectangular member. The shaft passes through the central aperture of thegenerally rectangular member. The retroreflective target is connected tothe shaft at an axial end of the shaft. At least one weight is connectedto the shaft so that the shaft when in a vertical position exerts adownward force against the retroreflective target in the vertical axialdirection of the shaft. The laser target assembly is positionable upon asurface at each of plural locations of the surface whereby the legs andthe retroreflective target are contiguous the surface, and wherein ateach location of the surface the retroreflective target is contiguousthe surface in accordance with the downward force exerted by at leastone weight.

According to exemplary embodiments of an inventive laser target device,also referred to herein as an inventive “bore tool,” a cradle holds anSMR (spherically mounted retroreflector) in constant tension (e.g., in aspring-loaded and/or weight-loaded manner) against an inner bore surfaceof an object to be measured in order to use laser tracking to determinesurface profile of the object. The inventive cradle includes a body,four legs, a shaft, and a coil spring. Based on the thickness of theobject being measured and/or the position of the SMR with respect to theobject, various geometric and potential characteristics are inventivelydeterminable such as inner diameters, corrosion, straightness, andflatness. Exemplary inventive practice allows for quicker data captureswith greater accuracy, as compared with current methods.

The present invention can be practiced so as to involve spring-loadingand/or weight-loading. According to an exemplary inventive embodimentthat involves both spring-loading and weight-loading, the spring-loadingand the weight-loading act in concert to impose a downward pressure sothat the laser tracking target at the bottom end of the shaft ismaintained in a state of constant contiguity with respect to theunderlying surface of the object being measured.

An inventive cradle is capable of holding an SMR in constant tensionagainst the inner surface of a cylinder or tube or any other structurewith an internal feature. The cradle allows the SMR to move freely in avertical axis in order to capture the surface profile accurately. Theframe of the cradle minimizes the lateral motion of the SMR to keep therecorded data along the center plane of the cradle. The weight of thecradle is such that gravity will keep the inventive bore tool along thecenter plane of the cradle. According to some inventive embodiments, amagnetic mount keeps the SMR housing connected to the cradle. The terms“cradle” and “carriage” are interchangeably used herein in contexts ofdescribing the present invention.

An inventive bore tool can be displaced in various ways, such as bybeing mechanically pulled through the bore, either via human or motorpower. Alternatively, the inventive bore tool itself can be providedwith motor-driven capability. The selected technique for relocating theSMR may depend on the length of the bore. According to some inventiveembodiments, the cradle is adjustable to conform to the shape of thebore that is to be measured.

Exemplary inventive practice provides an inner bore metrology tool thatis used to determine numerical data relating to the inner surface of atube or cylinder or other three-dimensional shape characterized by atleast one interior surface region. A laser tracker is implemented foracquiring the numerical data. According to exemplary effectuation ofquantitative data capture, a laser tracker shoots out a laser beam thathits the center of an SMR being held by an inventive bore tool. Some ofthe laser light is reflected by the SMR back to the tracker; thisreflected light informs the tracker as to the exact position of the SMR.While the inventive bore tool moves, the laser tracker constantly orrepeatedly records the new position of the SMR as detected via the laserbeam. The inventive boor tool ensures that the SMR is at all timespressed against a surface of the geometric object of measurementinterest.

Although a hollow cylindrical object is emphasized herein by way ofexample, the inventive methodology can be applied to measure practicallyany geometric object of interest. The object can be linear orcurvilinear, and can be polyhedral or non-polyhedral (e.g., with flatand/or curved surfaces). Geometric shapes that may be suitable forinventive practice include but are not limited to rectangular prism(e.g., cube), nonrectangular prism (e.g., triangular prism), pyramid,sphere, ellipsoid, cylinder, torus, cone, and a variety of irregularshapes.

Conventional metrological practice provides for iterative placement of aspring-loaded touch probe at discrete locations of a bore, wherein theprobe is situated at a single location for a measurement and issubsequently resituated at a different location of the bore for the nextmeasurement. In contrast, through use an inventive bore tool inassociation with a laser tracker, a practitioner can obtain results at agreater number of points along a bore in a much shorter time and withgreater accuracy.

Many modem laser trackers allow for the creation of a virtual plane downthe axis of a bore, thus easing data recordation in a very tight band.In addition, a bore can be rotated with an inventive bore tool in place,and a practitioner can determine the true longitudinal axis along theentire bore by capturing various cross-sections throughout the length ofthe bore.

Some inventive embodiments provide for adjustable legs of the cradle.Adjustability of the legs can be with respect to leg length and/or legangle. For instance, the cradle legs can be expandable and contractibleto suit bores of different sizes. Furthermore, inventive practice canprovide for adjustments of the angularities of the cradle legs forsimilar purposes. An ordinarily skilled artisan who reads thisdisclosure will appreciate various known mechanisms and techniques forimparting angular adjustability to leg in practicing the presentinvention.

The term “rod,” as used herein in describing the present invention,broadly refers to any elongate structure suitable for effectingmechanical connection between a body and an SMR, and for acting in aspring-loading manner in concert with a helical (coil) spring coaxiallyadjoining the rod. According to some embodiments of the presentinvention, an inventive rod is longitudinally adjustable similarly assome conventional probes are longitudinally adjustable. The probe-likerod is adjusted to and set at a selected length. For instance, aprobe-like rod is adjusted initially to determine the inner diameter,and this determination ensures best representation by the SMR of thesurface contour. An ordinarily skilled artisan who reads this disclosurewill appreciate various known mechanisms and techniques for impartinglongitudinal adjustability to a rod in practicing the present invention.

The ordinarily skilled artisan who reads this disclosure will appreciatethat multifarious combinations of leg lengths and leg angles arepossible in inventive practice, in order to suit the shape orconfiguration of the surface upon which the inventive device is mobile.An inventive embodiment can have all equal leg angles and all equal leglengths, or all equal leg angles and two or more unequal leg lengths, orall equal leg lengths and two or more unequal leg angles; or two or moreunequal leg angles and two or more unequal leg lengths.

An important inventive principle is that the vertical rod of aninventive device constantly applies a downward vertical force upon asurface beneath the inventive device. Since the vertical rod constantlyapplies a downward force, an object (e.g., a retroreflective sphere)attached at the bottom of the vertical rod) constantly applies adownward vertical force upon a surface underneath the inventive device,and hence maintains a constant contiguity with respect to the surface.According to various inventive embodiments, the downward force thatbrings about the downward pressure by the rod is accomplished using (i)a spring (e.g., metal spring), or (ii) one or more weights (e.g., metalweights), or (iii) a combination of a spring and one or more weights.

Inventive practice provides for use of one or more weights in lieu of orin addition to the spring, thereby maintaining pressure against asurface, such as the inner surface of an object having an interior void.One or plural weights can be associated with the vertical rod, and/orwith one, two, three, or all four legs. Particularly when one or moreweights are used, the fragility of the surface upon which an inventivedevice sits and moves (e.g., an inner surface such as that of an innerbore) should be taken into consideration by a practitioner of thepresent invention.

It is desirable to apply enough force downwards to maintain a contact ofthe target with the surface. At the same time, it is undesirable toapply too much pressure, i.e., so much pressure that it actually altersthe surface from its existing state. An important guideline for apractitioner of the present invention is to keep the center of gravityof the inventive device as low as possible. This is especiallysignificant for inventive embodiments implementing one or more weights.According to frequent inventive practice, a weight that is shaped as aflat cylinder may be beneficial insofar as promoting a low and stablecenter of gravity.

The examples of inventive practice that are described herein focus uponapplications involving laser tracking. Nevertheless, the presentinvention may be propitiously practiced in a variety other applications.An inventive device is positionable upon a surface whereby its legs andan object attached at the bottom of the vertical rod contact thesurface. Downward loading is exerted by at least one weight upon theattached object, and/or tension is exerted by a vertical spring upon theattached object. Accordingly, regardless of whether the inventive deviceis stationary or moving, the attached object at the bottom of thevertical rod presses against the surface below with constancy,maintaining consistently forceful contact therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, wherein like numbers indicatesame or similar parts or components, and wherein:

FIG. 1 is an elevation view of an embodiment of a laser target carrierin accordance with the present invention. As shown in FIG. 1, theinventive carrier is spring-loaded and is carrying a sphericalretro-reflective target.

FIG. 2 is an elevation view of the inventive carrier and theretroreflector target carried by the inventive carrier as shown inFIG. 1. As shown in FIG. 2, the inventive carrier and accompanyingretroreflective target are reduced in size and contextualized inside ahollow cylinder.

FIG. 3 is a perspective view of the inventive carrier and accompanyingretroreflective target shown in FIG. 1.

FIG. 4 is a perspective view of an embodiment of a laser tracking systemin accordance with the present invention. As shown in FIG. 4, accordingto the inventive tracking system a laser tracker emanates a laser beamthat hits the retrorefective target being carried by the inventivecarrier as shown in FIG. 1.

FIG. 5 is a top plan view of the inventive carrier shown in FIG. 1.

FIG. 6 is a partial and enlarged top plan view of the inventive carriershown in FIG. 1, particularly illustrating the main body having anaperture and the vertical rod passing through the aperture.

FIG. 7 is a partial and enlarged top plan view of the inventive carriershown in FIG. 1, particularly illustrating the vertical spring and thevertical rod encompassed by the vertical spring.

FIG. 8 is a diagram illustrating an example of coupling and uncouplingof a laser target (e.g., an SMR) with respect to a laser target cradle,in accordance with the present invention.

FIG. 9 is diagram showing examples of various leg lengths and leg anglesthat angles are possible in inventive practice, depending on theinventive embodiment.

FIG. 10 is a diagram illustrating variability of either leg length orleg angle or both leg length and leg angle, such variability possiblebetween any two legs of an inventive device, depending on the inventiveembodiment.

FIG. 11 is an elevation view, similar to the view of FIG. 1, of anotherembodiment of a laser target carrier in accordance with the presentinvention. As shown in FIG. 11, the inventive carrier is weight-loadedatop the vertical rod and is carrying a spherical retro-reflectivetarget.

FIG. 12 is a perspective view, similar to the view of FIG. 3, of theinventive carrier and accompanying retroreflective target shown in FIG.11.

FIGS. 13 through 17 are elevation views, similar to the views of FIG. 1and FIG. 11, of various inventive embodiments of a weight-loaded lasertarget carrier. One or more weights can be attached atop the verticalrod, and/or atop the body, and/or along the vertical rod, and or alongat least one leg.

FIG. 18 is an elevation view, similar to the views of FIGS. 1, 11, and13 through 17, of another embodiment of a laser target carrier inaccordance with the present invention. As shown in FIG. 18, theinventive carrier is spring-loaded, and is weight-loaded atop thevertical rod, and is carrying a spherical retro-reflective target.

FIG. 19 is a perspective view, similar to the views of FIGS. 3 and 12,of the inventive carrier and accompanying retroreflective target shownin FIG. 18.

FIG. 20 is an elevation view, similar to the views of FIGS. 1, 11, and13 through 18, illustrative of various possible ways and configurationsof combining spring-loading with weight-loading in accordance with thepresent invention. As shown in FIG. 18, the inventive carrier isspring-loaded, and is weight-loaded, and is carrying a sphericalretro-reflective target. In terms of weight-loading, one or more weightscan be attached atop the vertical rod, and/or atop the body, and/oralong the vertical rod, and/or along at least one leg.

FIG. 21 is a plan view of an example of a solid weight suitable forimplementation atop a vertical rod in accordance with the presentinvention. The vertical rod is shown as a circular dashed line beneaththe solid weight if conceived to be transparent.

FIG. 22 is a plan view of an example of an annular weight suitable forimplementation at a location along the length of a vertical rod inaccordance with the present invention.

FIG. 23 is a plan view similar to the view of FIG. 21. The solid weightshown in FIG. 23 has a smaller diameter than has the solid weight shownin FIG. 21.

FIG. 24 is a plan view similar to the view of FIG. 22. The annularweight shown in FIG. 24 has a smaller diameter than has the annularweight shown in FIG. 22.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring now to the figures, laser target device 100 includes straightvertical rod 110, coil spring 120, retroreflective target 130, body 140,and four obliquely angled legs 150. The inventive device 100 isdichotomized into two components, viz., (i) a laser target 130 and (ii)a laser target carriage (cradle) 160 for holding laser target 130.Target carriage 160 includes the straight vertical rod 110, the spring120, the body 140, and the four legs 150. As illustrated in FIG. 8,target carriage 160 and retroreflective target 130 are coupled to forminventive laser target device 100. Retroreflective target 130 is, forexample, a spherically mounted retroreflector (SMR) describing aspheroidal or approximately spherical shape.

Rod 110 is preferably made of a strong rigid material such as a suitablecomposite or steel or other suitable metal. Coil spring 120 ispreferably a helical metal spring such as made of spring steel. Body 140and legs 150 can be made of a variety of metal (e.g., steel oraluminum), polymeric (e.g., plastic), or composite (e.g.,nylon-reinforced plastic or other fiber-reinforced matrix) materials.Depending on the inventive embodiment (e.g., the environment of the datacapture), any of diverse materials can be used for the parts andcomponents of inventive device 100.

Spring 120 has an upper spring end 121 and a lower spring end 122. Rod110 has an upper rod end 111, a lower rod end 112, an upper rod portion113 and a lower rod portion 114. Upper rod portion 113 is bounded byupper rod end 111 and is uncircumscribed by coil spring 120. An upperpart of upper rod portion 113 is bounded at the top by upper rod end 111and projects above upper body surface 141 of body 140. Lower rod portion114 is bounded at the bottom by lower rod end 112 and is circumscribedby spring 120.

As depicted in FIGS. 1 through 3, inventive device 100 is positionedwithin a hollow cylindrical object 200, which has a longitudinalgeometric axis c, an inside cylindrical surface 201, and an outsidecylindrical surface 202. Carriage 160 holds target 130 in place so as topress target 130, in a spring-force manner via spring 120, against thearea of the inside surface 201 upon which inventive device 100 issituate. Each leg 150 includes a straight stem 151 and a spheroidal orapproximately spherical foot 152. Target 130 is spring-forcefullymaintained pressing downward against inside cylindrical surface 201whereby: the respective four feet 152 of the four legs 150 are sittingupon inside cylindrical surface 201; upper spring end 121 pressesagainst a bottom surface 142 of body 140; lower spring end 122 pressesagainst a top surface 131 of target 130.

Accordingly, carriage 160 is coupled with target 130 at the bottom 112of vertical rod 110 whereby the top 121 of spring 120 pushes against thebottom 142 of body 140 and the bottom 122 of spring 120 pushes againstthe top 131 of target 130. Supported by legs 150, target 130continuously adjusts in height (vertical position along axis a) so thatthe bottom 132 of target 130 remains in constant spring-tension contactwith inner cylindrical surface 201, which is the surface on whichinventive target device 100 is situate, either moving or stationary.

Reference now being made to FIG. 3 and FIG. 4, laser tracker 300 directslaser beams 310 at target 130, and receive laser retroreflections 320from target 130, at various locations of target 130 upon innercylindrical surface 201. At selected locations of carriage 160 (andcorrespondingly of target 130), laser beams 310 are emitted by lasertracker 300 and laser retroreflective beams 320 are received by lasertracker 300. These measurements can be conducted while carriage 160 isstationary or moving.

The ordinarily skilled artisan who reads the instant disclosure willappreciate the various ways in which movability upon inner cylindricalsurface 201 can be imparted to inventive target device 100, such asinvolving electromechanical propulsion. For instance, inventive targetdevice 100 can be pushed to or pulled from various locations viaexternal device. Optionally, inventive device can be repositioned “theold-fashioned way” upon inner cylindrical surface 201, viz., manually.

As another example, carriage 160 can contain a remotely controllablemotor for effecting movement via small wheels 159 respectfully housed infeet 152 such as shown in FIG. 8. For example, an inventive carriage 160can have two front wheels 159, or two back wheels 159, or four wheels159. The bottom of each wheel 159 is approximately even with or slightlybelow the bottom of the associated foot 152. Each wheel 159 can bevertically placed within its foot 152. In addition, planar-axisrotatability of wheel 159 within its foot 152 can be provided tomaintain verticality of wheel 159 in accordance with variation in legangle α.

Particularly with reference to FIG. 5, four legs 150-viz., legs 150A,150B, 150C, 150D—are connected to a lower portion of body 140 andproject downward and obliquely outward. Body 140 is shown to have arectangular plan profile. The four legs 150 are arranged in arectangular configuration not unlike that which characterizesautomobiles, carts, wagons, and other conventional land vehicles. Leg150A includes stem 151A and foot 152A. Leg 150B includes stem 151B andfoot 152B; leg 150C includes stem 151C and foot 152C; leg 150D includesstem 151D and foot 152D. The four legs 150 are connected at the fourrectangular corners of body 140; more specifically, the respective fourstems 151 are attached at the corner locations of body 140.

As illustrated in FIG. 2 and FIG. 6, vertical rod 110 of carriage 160 ischaracterized by a vertical geometric axis a. Retroreflector 130 isspheroidal and is attached to rod 120 at the lower rod end 112. Coilspring 120 generally describes a cylindrical shape and encompasses alower portion of rod 120. Accordingly, spring 120 and retroreflector 130are each similarly characterized by vertical axis a, and in factgenerally the entire inventive device 100 is characterized by symmetryabout vertical axis a. Inventive device 100 is also characterized by avertical geometric bisector plane p, in which vertical axis a lies.

The four legs 150 are each angled obliquely at the same angle α withrespect to bisector plane p. Angle α can vary in inventive practice,depending on the inventive embodiment. According to exemplary inventivepractice, leg angle α is greater than or equal to zero degrees and lessthan or equal to ninety degrees; that is, 0°≤α≤90°. Hence, depending onthe inventive embodiment, one or more legs 150 can have a verticallongitudinal axis s (α=0°) or a horizontal longitudinal axis s (α=90°).Nevertheless, according to more usual inventive practice, leg angle α isgreater than zero degrees and less than ninety degrees; that is,0°<α<90°. According to many embodiments and applications of the presentinvention, leg angle α falls within a leg angle α range between fifteendegrees inclusive and seventy-five degrees inclusive; that is, theangular range for these inventive embodiments is 15° α≤75°. According tomany inventive embodiments, all four values of leg angle α are equalduring laser tracking implementation of inventive target device 100.

As shown in FIG. 8, rod 110 has a length r, and each leg 150 has alength s. Some embodiments of the present invention are attributed withadjustability with respect to one, two, or all three of the following:leg angle α; rod length r; leg length s. The ordinarily skilled artisanwho reads the instant disclosure will appreciate the various mechanismsand techniques—such as involving telescoping, locking, folding, etc.—forproviding adjustability of rod 110 length r and/or leg 150 length s.Many inventive embodiments having adjustable leg length s will providethis capability for each of the four legs 150. Furthermore, theordinarily skilled artisan who reads the instant disclosure willappreciate the various mechanisms and techniques, such as involvingpivoting—for providing adjustability of leg angle α. Many inventiveembodiments having adjustable leg angle α will provide this capabilityfor each of the four legs 150.

Frequent inventive practice thus provides for all four legs 150 havingthe same leg angle α and the same leg length s. However, also withreference to FIGS. 9 and 10, the present invention can be practicedwhereby: all four legs 150 have the same leg length s and equal legangles α; or all four legs 150 have the same leg length s and two ormore legs 150 have unequal leg angles α; or all four legs 150 have thesame leg angle α and two or more legs 150 have unequal leg lengths s; ortwo or more legs 150 have unequal leg angles α and two or more legs 150have unequal leg lengths s. Inequality of leg angles α and/or leglengths s may be especially propitious for inventive practice withrespect to some non-cylindrical surfaces. For instance, with respect toa geometric surface characterized by a step, it may be beneficial toimplement an inventive device having leg angles α that are equal on thesame side of bisector plane p (shown in FIG. 5) and are unequal onopposite sides of bisector plane p, thus facilitating contiguity oftarget 130 with respect to the step.

Particularly as illustrated in FIGS. 5 through 7, body 140 has avertical central through-hole 143 bounded by a cylindrical inside holesurface 144. Rod 110 has a cylindrical outside rod surface 114. Thediameter of through-hole 143 is slightly larger than the diameter of rod110. Accordingly, rod 110 can fit inside through-hole 143 and translatetherein up-and-down along vertical axis a. For instance, rod 110 canslide up-and-down through through-hole 142 whereby outside rod surface114 contacts inside hole surface 144 at interface 145 with a low amountof friction, and thus there is sufficient freedom of vertical motion andno (or insignificant) lateral movement of rod 110.

Rod 110 at its lower end 112 is joined with target 130 at its uppersurface 131 at a junction 210, such as shown in FIG. 8. For instance,rod 110 and target 130 can be adhesively or magnetically joined wherebythe adhesive or magnetization is present on rod 110 or target 130.According to some inventive embodiments, inventive device 100 furtherincludes weights 220 (e.g., made of steel or other metal), which areadded to rod 110 and/or legs 150 of inventive device 100 in order tolower the center of gravity of inventive device 100, thereby preventingrotation of inventive device 100. As shown by way of example in FIG. 8,four equal weights 220 can be respectively attached to the four legs 150at corresponding locations.

Three main modes of practice of the present invention are those thatinvolve: (i) spring-loading of a target; (ii) weight-loading of atarget; (iii) both spring-loading and weight-loading of a target.Spring-loaded inventive practice is exemplified, e.g., in FIGS. 1 and 3;an inventive device 100 according to this mode is more specificallydesignated herein inventive device 100S. Generally speaking, theinventive principles described with reference to FIGS. 1 through 10 areapplicable to all three modes of inventive practice. Weight-loaded (butnot spring-loaded) inventive practice is exemplified in FIGS. 11 through17 and 21 through 24; an inventive device 100 according to this mode ismore specifically designated herein inventive device 100W. Combinedweight-loaded and spring-loaded inventive practice is exemplified inFIGS. 8 and 18 through 20; an inventive device 100 according to thismode is more specifically designated herein inventive device 100S.

With reference to FIGS. 11 through 20, one or more weights 170 can bemade part of an inventive target-carrying device 100 in order to exertdownward loading upon target 130. A weight 170 that is coupled withvertical rod 110 is more specifically designated herein weight 170R. Aweight 170 that is coupled with a leg 150 (e.g., with stem 151) is morespecifically designated herein weight 170L. A weight 170 that is coupledwith vertical rod 110 and/or body 140 so as to sit atop body 140 is morespecifically designated herein weight 170X. A weight 170R that iscoupled with vertical rod 110 atop vertical rod 110 is more specificallydesignated herein weight 170RT. A weight 170R that is coupled withvertical rod 110 at an axial-lengthwise location of vertical rod 110 ismore specifically designated herein weight 170RL.

Inventive practice is possible in any combination of one or more rodweights 170R, leg weights 170L, and body weights 170X, viz.: at leastone weight 170R; at least one weight 170L; at least one weight 170X; atleast one weight 170R and at least one weight 170L; at least one weight170R and at least one weight 170X; at least one weight 170R and at leastone weight 170X; at least one weight 170R and at least one weight 170Land at least one weight 170X.

According to usual inventive practice, weight 170RT is a solidaxisymmetric object of uniform density; weights 170RL, 170L, and 170Xare each a solid axisymmetric object of uniform density having athrough-hole or aperture to accommodate a vertical rod 110 passingtherethrough. According to frequent inventive practice, weights 170 aresolid or hollow cylinders. A weight 170 can be attached to a verticalrod 110 or a leg 150 or a body 140 mechanically (e.g., using bolts),adhesively, and/or magnetically. Grooves, holes, or other configurativefeatures can be provided in weights 170 and/or rod 110 and/or leg 150 toafford compatible coupling. According to some inventive embodiments, theinventive device's vertical rod 110 has, at the top 111 of vertical rod110, a tapped central hole (such as hole 190 shown in FIGS. 21 and 23)that extends a relatively short distance into vertical rod 110 in thedirection of axis a, thereby allowing for various weights 170RT to beattached via a bolt or other fastener. Weight 170RT may also be providedwith a central opening to further such attachment.

As shown by way of example in FIGS. 11 and 12, weight 170R can be asolid cylindrical weight (e.g., a solid disk or disk-like short solidcylindroid) such as weight 170RT attached atop vertical rod 110, e.g.,adjoining rod upper-end 111. FIG. 13 shows an example wherein weight170R is an annular weight 170RL (e.g., a collar or ring or short hollowcylindroid) designed to fit around a shaft or other elongate cylindricalobject) attached at a selected location along the vertical axial lengthof rod 110. FIGS. 14 and 15 illustrate possible inventive embodimentswhereby one or plural solid cylinder weights 170RT and/or one or pluralannulus weights 170RL are associated with vertical rod 110, and/or oneor more of the weights 170R are vertically adjustable bi-directionallyalong axis a.

Inventive implementation is possible of both a top disk weight 170RT(such as shown in FIGS. 11 and 12) and at least one collar weight 170RLalong the length of rod 110, above and/or below body 140. As anotherexample, a weight-loaded inventive device 100W can be embodied wherebythe only source of weight-loading is from one or more leg weights 170L,such as cylindrical weights 170L shown in FIGS. 8, 16, 17, and twenty.FIGS. 18 through 20 illustrate various inventive combinations of aspring 120 with one, two, or all three types of weight 170 (170R, 170L,170X). Spring 120 can be combined with one or more of any weight 170type. However, according to usual inventive practice, no weight 170RL isplaced between body 140 and retroreflective object (e.g., SMR) 130 whena spring 120 is used.

Some inventive embodiments provide for adjustability of one or moreweights 170R. For example, one or more rod length weights 170RL can bemoved (e.g., adjusted) up or down in an axial-longitudinal directionsuch as along rod axis a. Additionally or alternatively, one or more legweights 170L can be moved (e.g., adjusted) up or down in anaxial-longitudinal direction such as along leg axis s. Sizes, shapes anddensities can vary, depending on the inventive embodiment. An inventivedevice 100W or 100SW can be embodied to provide for switching of weightsto different sizes and/or shapes and/or weight magnitudes and/ordensities. As another example, the weight of a vertical rod 110 can beadjusted by replacing congruent vertical rods 110 of different materialshaving different densities.

Different diameters of solid cylindrical weight 170RT are illustrated byweights 170RT and 170RT′ in in FIGS. 21 and 23, respectively. Differentdiameters of annular weight 170RL are illustrated by weights 170RL and170RL′ in in FIGS. 22 and 24, respectively. Different axial lengths ofsolid cylindrical weight 170RT are illustrated by weights 170RT and170RT′ in in FIGS. 15 and 16, respectively. Different axial lengths ofannular weight 170RL are illustrated by weights 170RL and 170RL′ in inFIGS. 15 and 16, respectively. Different diameters of annular weight170RL are illustrated by weights 170RL and 170RL′ in in FIGS. 15 and 16,respectively. According to some inventive embodiments, solid weights170RT and/or annular weights 170RL and/or annular weights 170L of sameor similar or dissimilar characteristics can be added or subtracted.

It is to be emphasized that, although weights 170 are portrayed ascylindrical in some of the figures, inventive practice is possiblewherein one or more weights 170 has a curved or curvilinear shape thatis axially-symmetrical but does not define a geometric cylinder.Examples of geometric three-dimensional shapes suitable for inventivepractice of a weight 170 include but are not limited to cylindrical(e.g., disk-shaped), spherical, toroidal, ellipsoidal, prolatespheroidal, oblate spheroidal, or rounded cylindrical (e.g., roundeddisk-shaped). A cylinder having a flattened or short-axial character isalso referred to herein as a disk. A non-cylindrical weight 170RL isshown by way of example in FIG. 17.

According to frequent inventive practice, each weight 170—whether it besolid rod-top weight 170RT, or annular rod-length weight 170RL, or legweight 170L—is characterized by axial symmetry and uniform density. Aweight can be made of, for instance, a metal, plastic, or compositematerial. Each weight 170 is associated with the inventive device 100Wso that the longitudinal axis characterizing weight 170 is aligned withor coincident with the longitudinal axis characterizing the elongatecomponent of the inventive device 100. For instance, a solid rod-topweight 170RT axially aligns with longitudinal axis a of rod 110. Anannular rod-length weight 170RL axially coincides with longitudinal axisa of rod 110. An annular leg-length weight 170L axially coincides withlongitudinal axis s of leg 150.

The present invention, which is disclosed herein, is not to be limitedby the embodiments described or illustrated herein, which are given byway of example and not of limitation. Other embodiments of the presentinvention will be apparent to those skilled in the art from aconsideration of the instant disclosure, or from practice of the presentinvention. Various omissions, modifications, and changes to theprinciples disclosed herein may be made by one skilled in the artwithout departing from the true scope and spirit of the presentinvention, which is indicated by the following claims.

What is claimed is:
 1. A laser tracking system comprising a laser targetassembly, said laser target assembly including a generally rectangularmember, four legs, a shaft, at least one weight, and a retroreflectivetarget, said generally rectangular member characterized by four cornersand a central aperture extending therethrough, said shaft characterizedby a shaft axis, said four legs each connected to said generallyrectangular member at each corner of said rectangular member, said shaftpassing through said central aperture, said retroreflective targetconnected to said shaft at an axial end of said shaft, said at least oneweight connected to said shaft so that said shaft when in a verticalposition exerts a downward force against said retroreflective target inthe vertical axial direction of said shaft, wherein said laser targetassembly is positionable upon a surface at each of plural locations ofsaid surface whereby said legs and said retroreflective target arecontiguous said surface, and wherein at each said location of saidsurface said retroreflective target is contiguous said surface inaccordance with said downward force exerted by said at least one weight.2. The laser tracking system of claim 1, wherein said laser targetassembly further includes a coil spring, said coil spring circumscribingsaid shaft so as to exert respective tensile forces against saidrectangular member and said retroreflective target, wherein at each saidlocation of said surface said retroreflective target is contiguous saidsurface further in accordance with spring-loading associated with saidcoil spring.
 3. The laser tracking system of claim 2, further comprisinga laser tracker for emanating laser light striking said retroreflectivetarget and for receiving laser light reflecting from saidretroreflective target.
 4. The laser tracking system of claim 1, whereinsaid shaft has a bottom said axial end and a top said axial end, saidretroreflective target is connected to said shaft at said bottom axialend of said shaft, and a said weight is connected to said shaft at saidtop axial end of said shaft.
 5. The laser tracking system of claim 1,wherein said shaft has a bottom said axial end and a top said axial end,said retroreflective target is connected to said shaft at said bottomaxial end of said shaft, and a said weight is connected to said shaft ata location intermediate said bottom axial end and said top axial end ofsaid shaft.
 6. The laser tracking system of claim 5, wherein said weightconnected to said shaft at said bottom axial end is an annulusencircling said shaft and sharing said shaft axis.
 7. A carriage for anobject, the carriage comprising: a body having a vertical through-holeand a body bottom, said body characterized by a vertical longitudinalgeometric plane; four legs attached to said body at said body bottom,each said leg oriented at an oblique angle outward with respect to saidvertical longitudinal geometric plane; a vertical rod characterized by avertical geometric axis and passing through said vertical through-holeso as to be moveable vertically up-and-down, said vertical rod having anupper rod end and a lower rod end, said vertical rod extending above andbelow said through-hole, said rod capable of attachment to an object atsaid lower rod end; a weight characterized by said vertical geometricaxis and attached to said vertical rod, said weight exerting downwardloading upon an attached object in the direction of said verticalgeometric axis.
 8. The carriage of claim 7, wherein the carriage ispositionable upon a surface whereby said legs and the attached saidobject contact said surface and whereby said downward loading is exertedby said weight upon the attached said object so that said object pressesagainst a surface below the attached said object.
 9. The carriage ofclaim 7, wherein the carriage further comprises a vertical springcharacterized by said vertical geometric axis and encompassing saidvertical rod, said vertical spring having an upper spring end and alower spring end, said vertical spring pressing upon said body bottom atsaid upper spring end, said vertical spring pressing upon the attachedsaid object at said lower spring end, said vertical spring exertingtension upon the attached said object in the direction of said verticalgeometric axis.
 10. The carriage of claim 9, wherein the carriage ispositionable upon a surface whereby said legs and said object contactsaid surface and whereby said downward loading is exerted by said weightupon the attached said object and said tension is exerted by saidvertical spring upon the attached said object so that said objectpresses against a surface below the attached said object.
 11. Thecarriage of claim 7, wherein said weight is situated either: atop saidvertical rod at said upper rod end; or at a location on said verticalrod that is between said lower rod end and said upper rod end, saidweight distanced from said lower rod end and distanced from said upperrod end.
 12. The carriage of claim 7 wherein said weight is a first saidweight characterized by said vertical geometric axis and attached tosaid vertical rod, the carriage further comprising a second said weightcharacterized by said vertical geometric axis and attached to saidvertical rod, each of the first said weight and the second said weightexerting downward loading upon the attached said object in the directionof said vertical geometric axis.
 13. The carriage of claim 12 wherein:the first said weight is situated atop said vertical rod at said upperrod end; the second said weight is situated at a location on saidvertical rod that is between said lower rod end and said upper rod end,the second said weight distanced from said lower rod end and distancedfrom said upper rod end.
 14. The carriage of claim 7, wherein each saidleg includes a straight stem and a spheroidal foot connected to saidstraight stem.
 15. The carriage of claim 7, wherein said legs areattached to said body in a rectangular arrangement that is bisected bysaid horizontal geometric plane, and wherein said legs are each orientedoutward at the same said oblique angle with respect to said horizontalgeometric plane.
 16. The carriage of claim 7, wherein at said bottom rodend said rod is magnetically attractive for effecting said attachment tosaid object at said lower rod end.
 17. A laser target device for use inassociation with a laser tracking apparatus, the laser target devicecomprising: a body having a vertical through-hole and a body bottom,said body characterized by a vertical longitudinal geometric plane; fourlegs attached to said body at said body bottom, each said leg orientedat an oblique angle outward with respect to said vertical longitudinalgeometric plane; a vertical rod characterized by a vertical geometricaxis and passing through said vertical through-hole so as to be moveablevertically up-and-down, said vertical rod having an upper rod end and alower rod end, said vertical rod extending above and below saidthrough-hole; a retroreflective target for receiving a laser beam from alaser tracking apparatus, said retroreflective target attached to saidrod at said bottom rod end; a weight characterized by said verticalgeometric axis and attached to said vertical rod, said weight exertingdownward loading upon an attached said object in the direction of saidvertical geometric axis.
 18. The laser target device of claim 17,wherein the laser target device is positionable upon a surface wherebysaid legs and said retroreflective target contact said surface andwhereby said downward loading is exerted by said weight upon saidretroreflective target so that said retroreflective target pressesagainst a surface below said retroreflective target.
 19. The lasertarget device of claim 17, wherein the laser target device furthercomprises a vertical spring characterized by said vertical geometricaxis and encompassing said vertical rod, said vertical spring having anupper spring end and a lower spring end, said vertical spring pressingupon said body bottom at said upper spring end, said vertical springpressing upon said retroreflective target at said lower spring end, saidvertical spring exerting tension upon the attached said retroreflectivetarget in the direction of said vertical geometric axis.
 20. The lasertarget device of claim 9, wherein the laser target device ispositionable upon a surface whereby said legs and said retroreflectivetarget contact said surface and whereby said downward loading is exertedby said weight upon said retroreflective target and said tension isexerted by said vertical spring upon said retroreflective target so thatsaid retroreflective target presses against a surface below saidretroreflective target.